Repairing Roofs on Older Michigan Homes: What Changes and Why

Newer houses are built to a code the roofer knows well: plywood or OSB sheathing, one layer of shingles, ice barrier at the eaves, metal drip edge. On an older house, every one of those can be different, and several may have been changed by earlier owners in different decades.

The National Park Service, in its guidance on historic roofs, says the area to examine most closely on an older roof is the substrate: the sheathing or battens under the roofing. It names the danger spots as the eaves, under any earlier patches, where roof planes meet, and at walls such as dormers. That matches what roofers find in West Michigan. The shingles are rarely the only story.

The practical effect is that repair quotes on older homes carry more conditions. A roofer can see the shingles and the attic before starting, but the condition of a board deck under two layers is often unknown until the first course comes off. Expect a good contractor to explain what might change and how it will be priced if it does.

Many older homes have been roofed over rather than torn off. You can often count layers at the edge of the roof, at a gable rake, or around a vent pipe. Some have asphalt over asphalt; some have asphalt over the original wood shingles.

Michigan's 2015 code sets firm limits on covering an old roof. Section R908.3.1.1 says a roof re-cover is not permitted where the existing roof has two or more applications of any type of roof covering, where the existing roofing is water soaked or has deteriorated to the point that it is not an adequate base, or where the existing covering is slate, clay, cement or asbestos-cement tile. Where new roofing over wood shingles would create a combustible concealed space, Section R908.4 requires the old surface to be covered with an approved material such as gypsum board or mineral fiber first.

For a repair, the rule matters in two ways. First, a patch on a roof with two layers must tie into both, which takes more care than patching a single layer, because water can travel between layers. Second, if the repair area is big enough that you are really re-roofing a section, the layers in that section should come off to the deck. That is also where deck rot hides.

Roof repairs on older homes usually involve time in the attic, either to trace a leak or to check the deck from below. Older attics have their own hazards, and they are not roofing hazards, so you should know about them before anyone starts.

Two materials change how work on an older house is done. Homes built before 1978 may have lead-based paint on fascia, soffits, trim and painted flashing, and the federal Renovation, Repair and Painting rule applies when paid work disturbs more than small areas of it. Older roofing products, including some asphalt shingles, felts, roof cements and asbestos-cement shingles, may contain asbestos.

Neither is a reason to panic. Intact roofing that stays intact during the work is handled very differently from material that is sanded, cut with a saw or broken up. What matters is that whoever does the work knows the age of the house, asks the question, and uses methods that keep the material intact. The guide's article on asbestos and lead in old roofing covers the Michigan and federal rules in detail.

Older does not mean worn out. A single layer of shingles in good shape over a sound board deck can take a repair as well as any newer roof. The calculation changes when the house has two layers already, when the deck shows rot in several places, or when every repair reveals another one underneath.

The Park Service makes the same point about historic buildings: maintenance costs tend to multiply once trouble starts, and repeated repairs can approach the cost of a new roof. On an older Michigan home, a full tear-off is also the one time every board of the deck can be seen and fixed, and ice barrier can be added at the eaves where the house may never have had it.